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Cheap Long Distance Wireless Networking
enkidu writes: "Over at this article on macintouch there are some people who show how to extend Apple's airport range to 7km using legal signal boosting antennae. Connections at 50km+ are also mentioned. With enough base stations, you could even build your own private ricochet network in your neighborhood. " This should work with any WaveLAN cards ...
looks like a fun hack.
is it legal to actually use it in this manner?
Yes. It is legal to use it in this manner. We in the village have one wireless link that uses old WaveLAN cards to shoot 5 miles (that's 8km). These frequencies are very picky. If you have trees in the way, you have to either use a higher gain antenna or cut the trees down. Snow can cause problems. However, despite the problems, it sure is a lot faster than a phone line, and cheaper on a monthly basis.
We're using 24dB dish mesh antennas on each end due to the tree problem. W/o the trees in the way, we could easily shoot the 5 miles with a simple yagi 15dB antenna on both ends.
Once we get out tower permit, we'll be putting up the anetenna to about 50' above the ground and, hopefully, switching back to the yagi and trying to bring on someone who is 8 miles away. Right now the antenna is only about 20' above ground level. We figured we'd need about 20-30 more to get above the trees. 10' above the roof is easy. 30-40' is much harder.
Ahem. Actually it is *NOT* FCC legal. It seems that there really are very few professional wireless networking people commenting on here, and to those of you who are reading this and feeling as pained as I, this reply is for you!
I will explain the regulations here and hopefully clear up a lot of other misconceptions as well.
The fines for this stuff, BTW, are very very large especially if you muss up and they get you for spurious emissions or accidentally putting out 10W of power or the like. And when you're blasting this thing over a radius of 3 miles, it's not like you're being quiet about it!
2.4 gHz Telephones, 802.11 Wireless Networking, various medical devices, and microwave ovens transmit in the public domain ISM band. This band is a 22Mhz frequency range centered at 2.4gHz. ISM-band equipment may have a total EIRP (Effective Isotropic Radiated Power) of 36dB.
This EIRP number is calculated as a maximum of 30dBi with up to 6dBm of gain at this power. The nice catch is that for every dBi of power you subtract, you can add 6dBm of gain!! This power output can actually be equivalent to about 4W of legal power depending on your antenna gain... as long as your dBi output is less than 30dBi.
So, regulation-wise, yes. It is possible to use 2.4gHz 802.11 radios to go up to 30 miles legally, but why cant you modify your WaveLan/AirPort to go 30 miles? The reason is this:
Because the ISM band is a public-use band, The radio, the antenna, the cable, and the amplification equipment MUST ALL BE CERTIFIED BY THE FCC AS A SINGLE UNIT!!! This means, that if a particular high-gain antenna and/or amplifier is certified to be attached to the Apple AirPort (of which there are none except its internal antenna) then you may legally use it.
The WaveLan range extender is certified for use with the WaveLan equipment, but the apple airport is not a lucent WaveLan Silver in the eyes of the FCC. Thus the wavelan range extender is not certified for use on the airport -- which is what the first modification describes.
The second modification describes attaching 'standard' antennas to the AirPort by manufacturing a special cable that will let you attach to the special connector on the WaveLan card. I should note here that the reason there is a special connector on this card is so that only certified antennas may be connected to it without voiding its warranty and lucent/apple's responsibility for its performance! Am I beginning to make sense here?
The point is simple. When you open the AirPort or your WaveLan card and attach antennas or amplification that is not certified for use with the radio, you are breaking the law. Now, I personally don't really believe in the "certified as a unit" crap the FCC dishes out on public frequency equipment, but it is still the law.
Now, to raise another point.
11Mb radios are currently all DSSS. There aren't any frequency hopping 11Mb radios yet, although the 802.11 standard provides for them. The DSSS radios may use channels that are 2mHz apart, giving them a total of 11 usable channels in the 22MHz ISM band. The problem with this is that there are only 3 non-overlapping channels So to all of you out there who just think that you can extend your range all to hell and back, don't be suprised when four other people in your zip code do the same thing and find that none of you can even use your DSSS WLAN's!
Frequency hopping is another story altogether. FHSS 802.11 radios operate at up to 2Mb and you can co-locate 17 of these radios in one room and you won't interfere! If you want to be very cool to other WLAN users in your area, do check out FHSS radios, as they are much more practical for most WLAN applications. Honestly, if speed wasn't such a big deal to everyone and their dog then we might not even have 11Mb wireless until the Frequency hopping hardware catches up.
Please be responsible with your 802.11! If you don't, you're going to turn the wireless networking industry back to licensed microwave transmitters, and you'll probably just piss yourself off because all the public spectrum is gone.
~GoRK